JP2013040063A - Method and device for manufacturing fiber-optic strand - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and a device for manufacturing a fiber-optic strand in which residual compressive stress is reliably and stably imparted to the surface layer of the bare-optical-fiber portion, that is, a fiber-optic strand having reliably and stably excellent bending resistance.SOLUTION: A bare optical fiber 16 pulled out from a fiber spinning heating furnace 14 is cooled and solidified, and when the surface temperature of the bare optical fiber 16 reaches ≤100°C, the surface layer only of the bare optical fiber 16 is caused to re-melt while applying tension to the bare optical fiber 16. The surface layer is then caused to re-solidify and coated with a resin to thereby obtain a fiber-optic strand 24 in which compressive stress exists in the surface of the bare optical fiber 16 in a state after tension release.

Description

  The present invention relates to a method and an apparatus for manufacturing a silica glass-based optical fiber, particularly a silica-based optical fiber having improved bending resistance by applying a residual compressive stress to the surface layer of the bare optical fiber. It relates to a method and a device.

  In general, as a method of manufacturing a silica glass-based optical fiber, an optical fiber preform made of silica-based glass is heated and melted in a heating furnace for spinning, and is drawn out from the heating furnace for spinning to be cooled and solidified. In general, a bare optical fiber is coated with a protective coating resin, taken up by a take-up machine, and wound around a bobbin. As a manufacturing apparatus applied to manufacture of such a silica glass-based optical fiber, depending on the drawing speed, if the drawing speed is slow, an apparatus as shown in FIG. 6 is used. If the drawing speed is high, In general, an apparatus as shown in FIG. 7 is used.

  The manufacturing apparatus shown in FIG. 6 uses a spinning heating furnace 14 for heating and melting an optical fiber preform 12 made of silica glass, and an optical fiber bare wire 16 drawn linearly from the spinning heating furnace 14 to the atmosphere. A cooling zone 18 for cooling and solidifying therein, a coating apparatus 20 for coating the cooled and solidified bare optical fiber 16 with a protective coating resin, and curing the resin coated by the coating apparatus And a take-up device 26 such as a capstan for taking up the optical fiber 24 in a state where the protective coating resin is cured, and an illustration for finally winding up the optical fiber 24. It is set as the structure provided with the winder which does not.

  On the other hand, in the manufacturing apparatus shown in FIG. 7, a forced cooling device 18 </ b> A is disposed in the cooling zone 18 between the spinning heating furnace 14 and the coating apparatus 20, and is drawn out linearly from the spinning heating furnace 14. The configuration is such that the bare optical fiber 16 is forcibly cooled by the forced cooling device 18A. The forced cooling device 18A is usually a double wall structure (jacket structure), cooled from the wall by a cooling medium such as cooling water, and the space through which the inner optical fiber bare wire 16 passes (cooling). In the space), a gas that has good thermal conductivity and does not adversely affect the material of the bare optical fiber 16, for example, a cooling gas such as He gas, is introduced to forcibly cool the bare optical fiber 16. Yes.

  In manufacturing an optical fiber by such an optical fiber manufacturing apparatus, an optical fiber preform (quartz glass preform) 12 that is a raw material of the bare optical fiber is 2,000 ° C. or higher in a spinning heating furnace 14. The glass fiber of the bare optical fiber 16 is solidified and drawn from the lower part of the spinning heating furnace 14 while being drawn as an optical fiber bare wire 16 in a high temperature state. Then, cooling is performed in the cooling zone 18 to a temperature at which coating is possible (cooling in the air or cooling by the forced cooling device 18A). The bare optical fiber 16 cooled to the required temperature is coated with a protective resin in an uncured state in the coating apparatus 20, and the coating resin is further heated and cured by the curing apparatus 22. It is cured by an appropriate curing means according to the type of resin, becomes an optical fiber 24 having a protective coating layer, and is pulled by the pulling device 26 through the turn pulley 28 at a predetermined speed. Further, the optical fiber 16 is normally wound by a winding device such as a bobbin through a dancer roller (not shown).

By the way, recently, development of an optical fiber having excellent bending loss characteristics, that is, an optical fiber having a small bending loss even in a state where a bending with a small bending diameter is applied has progressed, and even an apparatus using an optical fiber temporarily has a small size of 5 mmφ or less. A bending diameter may be given. On the other hand, when the optical fiber is bent into a loop shape, a coil shape, or other bent shapes, a tensile stress is generated outside the bent portion (outside of the bend). And if a bending diameter becomes small, the tensile stress which acts on the bending outer side of an optical fiber will become large in connection with it.
If the tensile stress at the bending portion of the optical fiber exceeds the breaking limit strength of the material, the optical fiber breaks from the bending portion. Even if the tensile stress of the bending part does not exceed the fracture limit strength of the material, if the bending is applied for a long time or if bending is repeated, the bending part will break due to fatigue failure. . Therefore, when it is assumed to be used in a mode with a small bending diameter, it is necessary that the bending resistance is excellent. As described above, the fracture at the bent portion is mainly due to the tensile stress acting on the outer side of the bend. Therefore, as one measure for improving the bending resistance, the outer side of the bend generated when the optical fiber is bent is used. It is conceivable to reduce the tensile stress.

  A technique for improving the bending resistance from the above viewpoint has already been proposed in Patent Document 1. According to the proposal in Patent Document 1, in the process of softening, melting, and continuously drawing (fibre-making) a glass base material, when the bare optical fiber is solidified, a tensile force is applied to the optical fiber for drawing. With the (tension) applied, the surface of the bare optical fiber is reheated again to soften and melt only the surface layer (thereby keeping the central portion solidified), and then the surface with the tension applied. It has been shown to resolidify the layer. In this method, by remelting only the surface layer of the bare optical fiber once completely solidified, not only can the micro cracks on the surface disappear, but also the bare optical fiber is drawn by the tension for drawing. Strain (tensile strain) is relaxed in the surface layer of the bare wire, and as a result, in a state where the tension is released, compressive stress remains in the surface layer. When an optical fiber having a residual compressive stress on its surface is bent in this way, the tensile stress generated in the outer surface layer of the bend is relaxed or offset by the residual compressive stress, so that even if the bending diameter is small, the bending The tensile stress acting on the outside is substantially reduced, and as a result, cracks and breaks due to bending are less likely to occur.

However, when the inventors conducted experiments on the method disclosed in Patent Document 1, it was found that there were the following problems.
That is, in Patent Document 1, after the optical fiber bare wire drawn from the spinning heating furnace is cooled and completely solidified, the surface of the bare optical fiber is reheated in the presence of tension to remelt the surface layer. It's just said that it should be done. The temperature of the bare optical fiber when the surface of the bare optical fiber is reheated to remelt the surface layer, for example, is described as being reheated in a state cooled to about 200 ° C., for example. It ’s just that. However, when the present inventors reheat the surface layer at the stage where the bare optical fiber is completely solidified and resolidify according to the method disclosed in Patent Document 1, the bare wire portion of the optical fiber after the tension is released. It has been found that there are many cases where residual compressive stress cannot be stably applied to the surface layer. In particular, when the surface layer is reheated and re-solidified at a stage where the optical fiber bare wire is cooled to a temperature as described as an example in Patent Document 1, that is, about 200 ° C., the light after tension release Residual compressive stress is not applied to the surface layer of the bare wire portion of the fiber strand, or the residual compressive stress is not applied uniformly throughout the length of the optical fiber, so that bending resistance is ensured and It was found that it could not be improved stably.

JP-A-1-301531

  The present invention has been made in view of the above circumstances, and an optical fiber strand in which a residual compressive stress is reliably and stably applied to the surface layer of the bare optical fiber portion, and therefore bending resistance is ensured. It is another object of the present invention to provide a method and an apparatus for manufacturing a stable and excellent optical fiber.

  As a result of various experiments and studies to solve the above-mentioned problems, the present inventors have finally determined that the temperature condition of the bare optical fiber surface when the surface layer of the bare optical fiber is remelted is the residual compression. It was found to be an important factor for applying stress reliably and stably. That is, when the surface temperature of the bare optical fiber was remelted, the surface temperature was over 100 ° C. when the surface temperature of the bare optical fiber was varied and the surface was heated and remelted. In the case of heating and remelting, the residual compressive stress is not stably applied after releasing the tension. On the other hand, if the surface is heated and remelted when the surface temperature is 100 ° C. or lower, the residual compression is released after releasing the tension. The inventors have newly found that stress can exist reliably and stably, and have made the present invention.

Specifically, the manufacturing method of the optical fiber according to the basic aspect (first aspect) of the present invention is:
A quartz optical fiber preform is heated and melted in a spinning heating furnace, and the molten preform is drawn out linearly from the spinning heating furnace and continuously cooled and solidified. In the method of manufacturing an optical fiber strand, which is coated to make an optical fiber strand, and further pulling the optical fiber strand continuously while applying tension by a take-up machine,
When the surface temperature of the cooled and solidified bare optical fiber becomes 100 ° C. or less, the surface of the bare optical fiber is reheated with the tension applied, and only the surface layer of the bare optical fiber After that, the surface layer is re-solidified, and then the resin coating is applied, whereby a residual compressive stress is applied to the surface layer of the bare optical fiber portion in a state where the tension is released. It is characterized by obtaining.
Here, “reheating the surface of the bare optical fiber to remelt only the surface layer of the bare optical fiber” means only the surface layer of the silica glass constituting the bare optical fiber. Heating above the temperature at which it softens and exhibits fluidity, in other words, heating the surface layer above the temperature at which the strain in the surface layer is removed, while curing the portion inside the surface layer This means that the state as it is, that is, the state where the distortion is not removed is maintained. Further, “re-solidify” means that the softened surface layer is re-cured by cooling to return to a non-fluid state.

  In the method of manufacturing an optical fiber in such an aspect, the surface of the bare optical fiber is reheated in a tensioned state in order to remelt only the surface layer of the bare optical fiber. By carrying out when the surface temperature of the bare wire is as low as 100 ° C. or less, compressive residual stress can be reliably and stably applied to the surface layer of the bare wire portion of the optical fiber after the tension is released. .

Moreover, the manufacturing method of the optical fiber strand by the 2nd aspect of this invention WHEREIN: In the manufacturing method of the optical fiber strand of the said 1st aspect,
The linear base material drawn out from the spinning heating furnace is cooled and solidified by cooling in the atmosphere, and the time from the drawing out of the spinning heating furnace to the start of the reheating is 2 seconds or more. It is characterized by this.

  The method for manufacturing the optical fiber of the second aspect is suitable when the drawing speed (drawing speed) is slow, for example, when the drawing speed is about 5 to 100 m / min. In other words, when the wire speed is slow, the bare optical fiber drawn from the spinning heating furnace can be cooled and solidified by cooling in the atmosphere. In that case, the surface temperature index of the bare optical fiber The elapsed time from the time of drawing out from the spinning heating furnace can be used, and if the elapsed time is 2 seconds or longer, it can be estimated that the surface temperature is 100 ° C. or lower. Therefore, when 2 seconds or more have elapsed, reheating is started to remelt only the surface layer, and then solidify again, thereby ensuring a compressive residual stress in the surface layer of the bare portion of the optical fiber after releasing the tension. And can be stably applied.

Moreover, the manufacturing method of the optical fiber strand by the 3rd aspect of this invention WHEREIN: In the manufacturing method of the optical fiber strand of the said 1st aspect,
The linear preform drawn from the spinning heating furnace is cooled and solidified by continuously passing through a forced cooling device, and the surface temperature of the bare optical fiber drawn from the forced cooling device is 100. The reheating is started when the temperature becomes equal to or lower than 0C.

  The method for manufacturing the optical fiber of the third aspect is suitable when the linear velocity is high, for example, when the linear velocity is about 100 to 1000 m / min. That is, when the linear velocity is high, it is desirable to forcibly cool the bare optical fiber drawn out from the spinning heating furnace by the forced cooling device. In that case, the bare optical fiber drawn from the forced cooling device is desirable. When the surface temperature of the wire reaches 100 ° C. or less, the reheating is started to remelt only the surface layer and to resolidify, thereby compressing residual in the bare portion of the optical fiber after releasing the tension. Stress can be applied reliably and stably.

Furthermore, in the fourth to sixth aspects of the present invention, an apparatus for carrying out the optical fiber manufacturing method described as the first to third aspects is defined.
That is, the optical fiber manufacturing apparatus according to the fourth aspect of the present invention is
A spinning heating furnace for heating and melting the optical fiber preform;
A cooling zone for forcibly cooling and solidifying the bare optical fiber drawn linearly from the spinning heating furnace;
A reheating device for reheating the surface of the cooled and solidified optical fiber bare wire when the surface temperature becomes 100 ° C. or lower to remelt only the surface layer;
A recooling zone for cooling and resolidifying the surface layer of the bare optical fiber remelted by the reheating device;
A coating apparatus for coating the bare optical fiber cooled in the recooling zone with a resin;
A take-up device for taking up the tension applied to the optical fiber in a state where the resin coated by the coating device is cured;
It is characterized by having.

An apparatus for manufacturing an optical fiber according to the fifth aspect of the present invention is the apparatus for manufacturing an optical fiber according to the fourth aspect.
The cooling zone is configured to cool the bare optical fiber in the atmosphere.

  The apparatus for manufacturing an optical fiber according to the fifth aspect is suitable when the linear velocity is low, for example, when the linear velocity is about 5 to 100 m / min. That is, in the manufacturing apparatus according to this aspect, as described in the second aspect, the linear base material drawn from the spinning heating furnace is cooled and solidified by cooling in the atmosphere, and is drawn from the spinning heating furnace. The time from the start of reheating to the start of the reheating can be 2 seconds or more, whereby the residual compressive stress is reliably and stably applied to the bare wire partial surface layer of the optical fiber after the tension is released. Can do.

An apparatus for manufacturing an optical fiber according to a sixth aspect of the present invention is the apparatus for manufacturing an optical fiber according to the fourth aspect.
A forced cooling device for forcibly cooling the bare optical fiber is provided in the cooling zone.

  The apparatus for manufacturing an optical fiber according to the sixth aspect is suitable when the linear velocity is high, for example, when the linear velocity is about 100 to 1000 m / min. That is, in the manufacturing apparatus of this aspect, as described in the third aspect, the optical fiber bare wire drawn out from the spinning heating furnace is forcibly cooled by the forced cooling apparatus, and the surface temperature is 100 ° C. The reheating is started at the time of the following, and only the surface layer is remelted and re-solidified, so that the compressive residual stress is reliably and stably applied to the bare portion of the optical fiber after the tension is released. Can be granted.

  According to the method for manufacturing an optical fiber of the present invention, a compressive residual stress can be reliably and stably applied to the surface layer of the bare wire portion as an optical fiber after release of tension, and thus a small bending Even when a bending of a diameter is repeatedly applied to an optical fiber, an optical fiber having a low risk of cracking or breaking from the outside of the bend, that is, an optical fiber excellent in bending resistance can be reliably and It can be manufactured stably. Moreover, according to the optical fiber manufacturing apparatus of the present invention, the optical fiber excellent in bending resistance can be manufactured on a mass production scale as described above.

1 is a schematic illustration showing an example of an apparatus for carrying out an optical fiber manufacturing method according to a first embodiment of the present invention. It is a schematic diagram for demonstrating the condition of the bare optical fiber in the process which manufactures the optical fiber strand by applying the optical fiber strand manufacturing method of the 1st Embodiment of this invention. It is a schematic diagram which shows an example of the apparatus for enforcing the optical fiber strand manufacturing method of the 2nd Embodiment of this invention. It is a graph which shows the residual compression stress provision condition by Example 1 and Comparative Example 1 of this invention. It is a graph which shows the residual compression stress provision condition by Example 2 and Comparative Example 2 of this invention. It is a schematic diagram which shows an example of the apparatus for enforcing the conventional optical fiber strand manufacturing method. It is a schematic diagram which shows the other example of the apparatus for enforcing the conventional optical fiber strand manufacturing method.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a diagram showing the overall configuration of an optical fiber manufacturing apparatus 10 for carrying out the optical fiber manufacturing method of the first embodiment of the present invention. In addition, the optical fiber strand manufacturing apparatus 10 shown by FIG. 1 is applied suitably when a line speed is slow.

  In FIG. 1, an optical fiber manufacturing apparatus 10 includes a spinning heating furnace 14 for heating and melting an optical fiber preform 12 made of, for example, quartz glass, and a downward linear shape from the spinning heating furnace 14. The cooling zone 18 for cooling and solidifying the bare optical fiber 16 drawn out to the surface, and the surface of the cooled and solidified bare optical fiber 16 are heated to remelt only the surface layer. A heating device 30; a recooling zone 32 for resolidifying the remelted surface layer; a coating device 20 for coating the bare optical fiber having the surface layer resolidified with a protective coating resin; To take out the curing device 22 provided as necessary to cure the resin coated by the device 20 and the optical fiber 24 in a state where the protective coating resin is cured. It has a configuration in which a pulling device 26 for loading the tensile force to the optical fiber 24 (tension).

  Here, in the case of the first embodiment, the cooling zone 18 is an area where the bare optical fiber 16 is air-cooled by passing it through the atmosphere. The recooling zone 32 is also an area where the bare optical fiber 16 is cooled by passing it through the atmosphere.

The length of the cooling zone 18 is such that the time required for the bare optical fiber 16 exiting the spinning heating furnace 14 to reach the inlet of the reheating device 30 can be secured for 2 seconds or more. It is set to an appropriate length according to the speed. In other words, it is determined that the bare optical fiber 16 is cooled by air in the cooling zone 18 for 2 seconds or more. In this way, the bare optical fiber 16 is cooled by air for more than 2 seconds from the time when it exits the spinning heating furnace 14 to the entrance of the reheating device 30, so that the bare optical fiber 16 when entering the reheating device 30. It has been confirmed by experiments by the present inventors that the surface temperature of the film becomes 100 ° C. or lower.
The reheating device 30 is, in essence, rapidly moving the bare optical fiber 16 to a temperature at which the surface layer is melted, that is, a temperature at which distortion is removed by softening and showing fluidity (for example, 1600 ° C. or more) A specific configuration is not particularly limited as long as it can be heated for a short time, but a CO ₂ laser apparatus is typical, and an electric furnace, an oxyhydrogen burner, or the like can also be used.

  In FIG. 1, one coating apparatus 20 and one curing apparatus 22 are provided. However, in some cases, the first coating apparatus and the first curing apparatus, the second coating apparatus, and the second coating apparatus are used. Of course, the two curing devices may be arranged in series so as to cover two layers, and even when one coating device and one curing device are provided as shown in FIG. A two-layer coating may be performed using a coating apparatus capable of two-layer batch coating. This also applies to the manufacturing apparatus (second embodiment) described later with reference to FIG.

  An optical fiber manufacturing method according to the first embodiment of the present invention using the optical fiber manufacturing apparatus of FIG. 1 will be described below with reference to FIG. In FIG. 2, the portions with dots indicate the melted portions of the optical fiber preform 12 and the bare optical fiber 16.

  In FIG. 1 and FIG. 2, the optical fiber preform 12 heated and melted at a high temperature of 2000 ° C. or higher in the spinning heating furnace 14 is lowered at the lower end of the spinning heating furnace 14 by the take-up force (tension) T from the take-up device 26. Is pulled out as a bare optical fiber 16 at a low speed of, for example, about 5 to 100 m / min, and the bare optical fiber 16 immediately passes through the cooling zone 18. While passing through the cooling zone 18, the bare optical fiber 16 is cooled by the atmosphere at about room temperature, the temperature is lowered, and the bare optical fiber 16 is solidified to the center in the middle, and further cooling proceeds. To do. The surface of the bare optical fiber 16 is heated by the reheating device 30 when two seconds or more have passed after leaving the spinning heating furnace 14, and therefore when the surface temperature of the bare optical fiber 16 becomes 100 ° C. or less. Thus, only the surface layer 16A is melted. That is, only the surface layer 16A from the surface to a predetermined depth is melted while the central portion 16B of the bare optical fiber 16 is kept solidified.

  Here, the tension T from the take-up device 26 acts on the entire bare optical fiber 16 solidified to the central portion 16B in the cooling zone 18, and tensile strain is generated due to the tensile stress. And since the surface layer 16A remelted by the reheating device 30 is softened and has fluidity, the tensile strain is once released, and the tension T from the take-up device 26 is only the center portion 16B that has not been remelted. Will be in a state to bear. Subsequently, the bare optical fiber 16 passes through the recooling zone 32 and is cooled from the surface by the atmosphere at room temperature, and the surface layer 16A is re-solidified. Thereafter, the bare optical fiber 16 passes through the coating device 20 and the curing device 22 and is coated with a protective coating resin to form an optical fiber 24 having a protective coating, and a tension T is applied by the take-up device 26. It is taken up while being wound around a winding device (not shown) such as a bobbin.

  Here, the tension T is applied to the bare optical fiber 16 and the optical fiber 24 during the period from the time when the fiber is pulled out of the spinning heating furnace 14 and solidifies in the middle of the cooling zone 18 to be taken out by the take-up device 26. It has been added. In particular, a tensile stress is accumulated in the central portion (the portion that has not been remelted) 16B of the bare optical fiber 16 because the tensile stress T continues to be generated by the tension T from the time of solidification until it is pulled off. Is done. On the other hand, the surface layer (remelted portion) 16A of the bare optical fiber 16 is temporarily relieved of tensile strain by the remelting, and then re-solidifies and then only some tensile strain remains. Accordingly, at the stage of being pulled by the pulling device 26, a large tensile strain remains in the central portion 16B of the bare optical fiber portion, and a smaller tensile strain remains in the surface layer 16A. When the tension T is released after the take-off, the optical fiber bare wire portion is elastically deformed in the direction in which the tensile strain (particularly the large tensile strain in the central portion) is released, that is, in the compression direction. 16B and the surface layer 16A have a large difference in the remaining tensile strain, and at the same time, the tensile strain of the central portion 16B disappears (or becomes smaller), and at the same time, a compressive stress is generated in the surface layer 16A. The compressive stress remains even after the tension is released. That is, the residual compressive stress is applied to the surface layer 16A. In this way, when the optical fiber strand in which the residual compressive stress is applied to the surface layer 16A of the bare optical fiber portion is subjected to bending, tensile stress is generated in the outer surface layer of the bending. Since there is pre-existing residual compressive stress, the tensile stress acting on the outer surface layer of the bend is offset by the residual compressive stress or at least relaxed by the residual compressive stress, so that It is effectively prevented that a crack is generated on the outer surface of the bending due to the applied tensile stress or a fracture occurs from the outer side of the bending. Therefore, even when the bending radius is small, excellent bending resistance is exhibited.

  Here, the cooling time in the cooling zone 18 is as short as 2 seconds or less, the cooling is insufficient, and the surface temperature when the surface layer of the bare optical fiber 16 is reheated is still high (100 ° C. or higher, for example, Patent Document 1). 200 ° C.), the center portion of the bare optical fiber 16 at that time is still at a considerably high temperature, so that the center portion is further heated by reheating. Therefore, even if it does not melt, the softening proceeds and the tensile strain at the central part is also relaxed, and as a result, it becomes difficult to provide a sufficient tensile strain difference between the surface layer and the central part, Even in the state after the tension is released, it becomes difficult to give a sufficient compressive residual stress to the surface layer. In addition, when the optical fiber bare wire is not sufficiently cooled until the surface temperature becomes 100 ° C. or less at the time of reheating for remelting the surface layer, there is a large variation in the temperature of the central part at the time of reheating. There is a large variation in the presence or absence of the tensile strain in the center and the degree of relaxation, and the tensile strain in the center is not relaxed at a certain position in the length direction of the bare optical fiber. At other positions, the tensile strain at the center is greatly relaxed, and as a result, the portion where residual compressive stress is applied to the surface layer and the portion where it is not applied in the longitudinal direction in the state where the tension is finally released. The bending resistance may vary in the length direction.

  However, it takes 2 seconds or more for the bare optical fiber 16 exiting the spinning heating furnace 14 to pass through the cooling zone 18 by air hollow cooling and reach the inlet of the reheating device 30, and the reheating device 30. If the surface is sufficiently cooled until just before the reheating by 100 ° C. until the temperature becomes a low temperature of 100 ° C. or less, the temperature of the central portion has already sufficiently decreased. A sufficient temperature difference from the surface can be ensured, and the temperature variation in the central portion is relatively small. Therefore, it is possible to prevent the tensile strain in the central portion from being relaxed and the variation in the tensile strain in the central portion can be prevented. Therefore, it is possible to ensure a large difference in tensile strain between the central portion and the surface layer in a tension load state, and to reduce variations in the difference in tensile strain so that the surface is finally released with the tension released. It is possible to sufficiently apply the residual compressive stress to the layer, and to reduce the variation in the residual compressive stress of the surface layer.

  FIG. 3 shows the overall configuration of an optical fiber manufacturing apparatus for carrying out the optical fiber manufacturing method of the second embodiment of the present invention. The optical fiber manufacturing apparatus shown in FIG. 3 is suitable when the linear velocity is high, for example, about 100 to 1000 m / min. In FIG. 3, the same elements as those shown in FIG. 1 are denoted by the same reference numerals as those in FIG.

  In the case of the apparatus of the second embodiment, a forced cooling device 18A is provided in a cooling zone 18 for cooling and solidifying the bare optical fiber 16 drawn from the spinning heating furnace 14. The cooling capacity of the forced cooling device 18A is controlled by the cooling control device 36, and its specific configuration is not particularly limited. In short, any cooling device capable of adjusting the cooling capacity may be used, for example, an optical fiber. As a double wall structure (jacket structure) surrounding the passing region of the bare wire 16, cooling is performed from the wall portion by a cooling medium such as cooling water, and heat is passed into the passing region (cooling space) of the inner optical fiber bare wire 16. A cooling gas that has good conductivity and does not adversely affect the material of the bare optical fiber 16, such as He gas, is introduced to cool the bare optical fiber 16, and the cooling gas introduction flow rate is controlled to be cooled. By controlling with the device 36, the cooling capacity for the bare optical fiber 16 may be controlled. Further, at a position below the forced cooling device 18A and immediately above the reheating device 30 (near the entrance of the reheating device 30), a surface temperature detecting device 34 for measuring the surface temperature of the bare optical fiber 16, for example, radiation A thermometer is provided. The surface temperature signal obtained by the surface temperature detection device 34 is sent to the cooling control device 36, and the cooling control device 36 controls the cooling ability of the forced cooling device 18A. A recooling zone 32 for recooling the bare optical fiber 16 in which only the surface layer has been remelted by the reheating device 30 is provided with a forced cooling device 32A for recooling. The specific configuration of the forced cooling device 32A for recooling is not particularly limited. For example, similarly to the forced cooling device 18A, a double wall structure (jacket structure) surrounding the passing region of the bare optical fiber 16 is used. In addition to cooling from the wall by a cooling medium such as cooling water, the inside of the inner optical fiber bare wire 16 passing region (cooling space) has good thermal conductivity and does not adversely affect the material of the optical fiber bare wire 16 A configuration may be adopted in which a cooling gas such as He gas is introduced to cool the bare optical fiber 16.

An optical fiber manufacturing method according to the second embodiment of the present invention using the optical fiber manufacturing apparatus shown in FIG. 3 as described above will be described.
In FIG. 3, the optical fiber preform 12 heated and melted at a high temperature of 2000 ° C. or higher in the spinning heating furnace 14 is, for example, 100 from the lower end of the spinning heating furnace 14 by the take-up force (tension) T from the take-up device 26. The optical fiber bare wire 16 is drawn linearly at a high speed of about 1000 m / min, and passes through the forced cooling device 18 </ b> A in the cooling zone 18. While passing through the forced cooling device 18A, the bare optical fiber 16 is forcibly cooled, the temperature rapidly decreases, and the bare optical fiber 16 is solidified to the center in the middle, and further cooling proceeds. . On the other hand, the surface temperature of the bare optical fiber 16 when entering the reheating device 30 is measured by the surface temperature detection device 34 disposed near the entrance of the reheating device 30 so that the temperature becomes 100 ° C. or less. Further, the cooling control device 36 performs feedback control of the cooling capacity of the forced cooling device 18A. For example, the flow rate of the cooling gas flowing into the cooling control device 36 is controlled according to the detected surface temperature. By such control, the bare optical fiber 16 is cooled so that its surface temperature becomes 100 ° C. or less, and at that stage, the surface is reheated by the reheating device 30 and only the surface layer is melted. That is, only the surface layer portion is melted while the central portion of the bare optical fiber 16 remains solidified.

Here, as in the case of the first embodiment shown in FIG. 1, the tension T from the take-up device 26 acts on the entire bare optical fiber 16 solidified to the central portion in the forced cooling device 18A. Since the tensile strain is generated and the surface layer remelted by the reheating device 30 is softened and has fluidity, the tensile strain is once released and the tension T from the take-up device 26 is remelted. Only the central part that has not been done is in a state to bear.
Subsequently, the bare optical fiber 16 passes through the forced cooling device 32 </ b> A in the recooling zone 32. In the forced cooling device 32A, the bare optical fiber 16 is forcibly cooled from its surface, and the surface layer is solidified again. Thereafter, the bare optical fiber 16 passes through the coating device 20 and the curing device 22 and is coated with a protective coating resin to form an optical fiber 24 having a protective coating, and a tension T is applied by the take-up device 26. While being taken up, it is taken up by a winding device (not shown) such as a bobbin.

  As described above, also in the manufacturing method of the second embodiment using the optical fiber manufacturing apparatus shown in FIG. 3, the reheating for melting only the surface layer of the bare optical fiber 16 is performed at a surface temperature of 100 ° C. Since the process is performed at a sufficiently cooled stage until the following temperature is reached, the center temperature at the time of reheating is sufficiently lowered as in the case of the first embodiment. The temperature at the center when heated is not so high, and the variation in the temperature at the center is relatively small, so that the tensile strain at the center can be relaxed, or the tensile strain at the center can vary. Therefore, a large difference in tensile strain between the central portion and the surface layer in a tension load state can be secured, and the variation in the difference in tensile strain is also reduced, and the tension is finally released. State Residual compressive stress in the surface layer can be sufficiently impart, moreover can be made smaller variation of residual compressive stress of the surface layer.

  In the above, the thickness (remelting depth) of the surface layer that reheats and remelts the bare optical fiber from the surface is not particularly limited, but the bare optical fiber diameter in a general-purpose communication optical fiber ( In the case of usually in the range of about 80 to 150 [mu] m, generally 125 [mu] m), it is preferable to remelt so that compressive strain is applied to a depth of about 2 to 10 [mu] m. When compressive strain is applied only to a portion having a depth of less than 2 μm, it may be difficult to apply sufficient residual compressive stress to improve bending resistance, while up to a portion exceeding 10 μm. If compressive strain is applied, the optical properties of the optical fiber may be affected.

  Examples of the present invention will be described below together with comparative examples. In addition, the following examples are for clarifying the effect of this invention, and of course, the conditions described in the examples do not limit the technical scope of this invention.

[Example 1]
Example 1 is an example in which the apparatus shown in FIG. 1 was used and the optical fiber manufacturing method of the present invention was implemented based on the first embodiment.
That is, in producing a silica glass based optical fiber strand (bare wire diameter 125 μm, strand finished outer diameter 250 μm) having a two-layer coating structure having the characteristics of a general single mode fiber, it is drawn from the heating furnace 14 for spinning. After the bare optical fiber 16 is cooled by air in the cooling zone 18, only the surface layer of the bare optical fiber is melted by the reheating device 30, and then the solidified layer is re-solidified in the recooling zone 32. Then, a protective coating layer made of an ultraviolet curable resin was formed, and an experiment was conducted by the take-up device 26 with a tension of about 100 gf. Here, the time from the lower end of the spinning heating furnace 14 to the reheating device 30, that is, the cooling time by the cooling zone 18 is changed at intervals of 0.5 seconds within the range of 2 seconds to 5 seconds, Further, the take-up speed (linear speed) was variously changed within a range of 5 to 100 m / min.
For each obtained optical fiber, when the residual stress of the bare wire partial surface layer after releasing the tension was examined, at any linear speed and any cooling time, over the entire length in the length direction of the optical fiber, It was confirmed that the residual compressive stress was almost uniformly applied to the bare wire surface layer. Typically, when the linear velocity is 20 m / min and the cooling time is 2 seconds, a residual compressive stress of about 50 MPa is applied to the bare wire partial surface layer after releasing tension almost uniformly in the length direction. It has been confirmed that Further, when bending was actually applied to the optical fiber strands to which these residual compressive stresses were applied, no breakage due to the application of bending occurred even at a bending diameter of 2.0 mmφ.
Here, as a criterion for the presence or absence of residual compressive stress, the surface residual compressive stress is measured using FSE (Fiber Stress Analyzer), and the measured value of the residual compressive stress is 5 MPa or more. It was determined that there was residual compressive stress, and when the residual compressive stress on the surface was less than 5 MPa, it was determined that there was no residual compressive stress.
In Example 1, it was confirmed that the surface temperature of the bare optical fiber at the entrance of the reheating device 30 is 100 ° C. or lower when the cooling time is 2 seconds or longer.

[Comparative Example 1]
In the same manner as in Example 1, a quartz glass-based optical fiber strand (bare wire diameter 125 μm, finished wire outer diameter 250 μm) having a two-layer coating structure having the characteristics of a general single mode fiber is used for spinning. The bare optical fiber 16 drawn out from the heating furnace 14 is air-cooled by the atmosphere in the cooling zone 18, and then only the surface layer of the bare optical fiber is melted by the reheating device 30. Then, a protective coating layer made of an ultraviolet curable resin was formed, and an experiment was conducted in which the film was pulled with a pulling device 26 at a tension of about 100 gf. Here, the time from the lower end of the spinning heating furnace 14 to the reheating device 30, that is, the cooling time in the cooling zone 18 is less than 2 seconds, that is, 0 to 1.5 to 0.5 seconds. .Changed at 5 second intervals. The take-up speed (linear speed) was variously changed within the range of 5 to 100 m / min, as in Example 1.
For each of the obtained optical fibers, the residual compressive stress of the bare wire partial surface layer after releasing the tension was examined. When the cooling time was 1.5 seconds, the optical fiber It has been found that there are a mixture of a portion to which the residual compressive stress is applied and a portion to which the residual compressive stress is not applied in the length direction, that is, there is a variation in the application status of the residual compressive stress. Further, when the cooling time was 1.0 seconds and 0.5 seconds, it was confirmed that no residual compressive stress was applied to the bare wire partial surface layer at any linear velocity.
In addition, when bending is actually applied to an optical fiber in which the residual compressive stress is not applied or the presence / absence of the residual compressive stress varies in the length direction, the optical fiber is bent to a bending diameter of 2.0 mmφ. In either case, it was confirmed that cracks or fractures occurred outside the bend.
In Comparative Example 1, it is confirmed that the cooling time is 1.5 to 0.5 seconds or more and the surface temperature of the bare optical fiber at the entrance of the reheating device 30 exceeds 100 ° C. .

  FIG. 4 shows a summary of the presence or absence of residual compression after tension release at each linear velocity and each cooling time in Example 1 and Comparative Example 1 described above. From FIG. 4, when the apparatus as shown in FIG. 1 is used, when the cooling time in the air in the cooling zone 18 is 2 seconds or more, it is manufactured at any linear velocity within the range of 5 to 100 m / min. However, it is clear that the residual compressive stress can be stably applied after releasing the tension.

[Example 2]
Example 2 is an example in which the apparatus shown in FIG. 3 was used and the optical fiber manufacturing method of the present invention was implemented based on the second embodiment.
That is, in producing a silica glass based optical fiber strand (bare wire diameter 125 μm, strand finished outer diameter 250 μm) having a two-layer coating structure having the characteristics of a general single mode fiber, it is drawn from the heating furnace 14 for spinning. After the optical fiber bare wire 16 is forcibly cooled in a forced cooling device 18A using He gas as a cooling gas, only the surface layer of the bare optical fiber is melted and then forcedly cooled in a recooling device 32A. The surface layer was re-solidified, a protective coating layer made of an ultraviolet curable resin was further formed, and an experiment was conducted with the take-up device 26 with a tension of about 100 gf. Here, the surface temperature of the bare optical fiber 16 at the entrance of the reheating device 30 is detected by the surface temperature detecting device 34 so that the surface temperature of the bare optical fiber 16 at that position becomes 100 ° C. or 50 ° C. The flow rate of the cooling gas (He gas) of the forced cooling device 32A was controlled. The take-up speed (linear speed) was variously changed within the range of 100 to 600 m / min.
When the compressive residual stress of the bare wire partial surface layer after releasing the tension was examined for each of the obtained optical fiber strands, light was obtained at any linear velocity and at any temperature (surface temperature at the inlet of the reheating device 30). It was confirmed that the residual compressive stress was applied almost uniformly over the entire length of the fiber strand in the length direction. Typically, when the linear velocity is 600 m / min and the surface temperature immediately before reheating is 100 ° C., the residual compressive stress of about 55 MPa is almost uniform in the length direction on the bare wire partial surface layer after releasing the tension. It was confirmed that it was granted.
Further, when bending was actually applied to the optical fiber strands to which these residual compressive stresses were applied, it was confirmed that no cracks or breaks occurred outside the bending until the bending diameter was about 2.0 mmφ.

[Comparative Example 2]
In the same manner as in Example 2, a quartz glass-based optical fiber strand (bare wire diameter 125 μm, finished strand outer diameter 250 μm) having a two-layer coating structure having the characteristics of a general single mode fiber is used for spinning. The bare optical fiber 16 drawn out from the heating furnace 14 is forcibly cooled in the forced cooling device 18A, and then only the surface layer of the bare optical fiber is melted. The sample was solidified, a protective coating layer made of an ultraviolet curable resin was formed, and an experiment was conducted by the take-up device 26 with a tension of about 100 gf. Here, the surface temperature of the bare optical fiber 16 at the entrance of the reheating device 30 is detected by the surface temperature detecting device 34 so that the surface temperature of the bare optical fiber 16 at that position becomes 150 ° C. to 5000 ° C. The flow rate of the cooling gas (He gas) of the forced cooling device 32A was controlled. The take-up speed (linear speed) was variously changed within a range of 100 to 1000 m / min.
When the residual compressive stress of the bare wire partial surface layer after releasing the tension was examined for each obtained optical fiber, the surface temperature of the bare optical fiber 16 at the entrance of the reheating device 30 was 150 ° C. In any linear velocity, there is a mixture of a portion where residual compressive stress is applied and a portion where no residual compressive stress is applied in the length direction of the optical fiber, that is, there is a variation in the state of application of residual compressive stress. It turned out to be. Further, when the surface temperature of the bare optical fiber 16 at the entrance of the reheating device 30 is 200 to 500 ° C., it is confirmed that no residual compressive stress is applied to the optical fiber at any linear velocity. It was.
In addition, when bending is actually applied to an optical fiber in which the residual compressive stress is not applied or the presence / absence of the residual compressive stress varies in the length direction, the optical fiber is bent to a bending diameter of 2.0 mmφ. In either case, it was confirmed that cracks or fractures occurred outside the bend.

  FIG. 5 shows a summary of the presence or absence of residual compression after tension release at each linear velocity and each cooling time in Example 2 and Comparative Example 2 described above. From FIG. 5, when using the apparatus as shown in FIG. 3, the surface temperature immediately before reheating is controlled to 100 ° C. or lower, so that it can be produced at any linear velocity within the range of 100 to 600 m / min. It is clear that the residual compressive stress can be stably applied after releasing the tension.

  DESCRIPTION OF SYMBOLS 10 ... Optical fiber manufacturing apparatus, 12 ... Optical fiber base material, 14 ... Heating furnace for spinning, 16 ... Bare optical fiber, 16A ... Surface layer, 16B ... Center 18: cooling zone, 18A: forced cooling device, 20 ... coating device, 24 ... optical fiber, 26 ... take-up device, 30 ... reheating device, 32. ..Recooling zone, 32A ... Forced cooling device, 34 ... Surface temperature detection device, T ... Tension.

Claims (6)

A quartz optical fiber preform is heated and melted in a spinning heating furnace, and the molten preform is drawn out linearly from the spinning heating furnace and continuously cooled and solidified. In the method of manufacturing an optical fiber strand, which is coated to make an optical fiber strand, and further pulling the optical fiber strand continuously while applying tension by a take-up machine,
When the surface temperature of the cooled and solidified bare optical fiber becomes 100 ° C. or less, the surface of the bare optical fiber is reheated with the tension applied, and only the surface layer of the bare optical fiber After that, the surface layer is re-solidified, and then the resin coating is applied, whereby a residual compressive stress is applied to the surface layer of the bare optical fiber portion in a state where the tension is released. A method for producing an optical fiber, characterized in that: In the manufacturing method of the optical fiber strand of Claim 1,
The linear base material drawn out from the spinning heating furnace is cooled and solidified by cooling in the atmosphere, and the time from the drawing out of the spinning heating furnace to the start of the reheating is 2 seconds or more. A method for manufacturing an optical fiber. In the manufacturing method of the optical fiber strand of Claim 1,
The linear preform drawn from the spinning heating furnace is cooled and solidified by continuously passing through a forced cooling device, and the surface temperature of the bare optical fiber drawn from the forced cooling device is 100. The method for manufacturing an optical fiber, wherein the reheating is started when the temperature becomes equal to or lower than 0C. A spinning heating furnace for heating and melting the optical fiber preform;
A cooling zone for forcibly cooling and solidifying the bare optical fiber drawn linearly from the spinning heating furnace;
A reheating device for reheating the surface of the cooled and solidified optical fiber bare wire when the surface temperature becomes 100 ° C. or lower to remelt only the surface layer;
A recooling zone for cooling and resolidifying the surface layer of the bare optical fiber remelted by the reheating device;
A coating apparatus for coating the bare optical fiber cooled in the recooling zone with a resin;
A take-up device for taking up the tension applied to the optical fiber in a state where the resin coated by the coating device is cured;
And an optical fiber manufacturing apparatus. The apparatus for manufacturing an optical fiber according to claim 4,
The apparatus for manufacturing an optical fiber, wherein the cooling zone is configured to cool the bare optical fiber in the atmosphere. The apparatus for manufacturing an optical fiber according to claim 4,
An apparatus for manufacturing an optical fiber, wherein a forced cooling device for forcibly cooling the bare optical fiber is provided in the cooling zone.

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